340 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



riorly in both upper and lower series. Talonid of M ? inclosing a small basin- 

 shaped area with a single high point on its posterior rim. Palate imperforate. 

 Mandibular symphysis ligamentous. Hallux reduced. Terminal phalanges 

 uncleft, laterally compressed and pointed. Cladosictis. 



(Miocene, Santa Cruz formation, Patagonia, C. lustratus, C. petersoni.) 

 3. Dental formula $, \, |, |. Protocone well developed on all the upper molars. 

 MA with protocone inclosing a basin-shaped area, paracone and antero-external 

 style large, metacone vestigial or absent. Upper premolars increasing regularly 

 in size posteriorly ; median and posterior lower premolars subequal. Talonid 

 of Mj large and strongly bicuspidate. Palate imperforate. Mandibular sym- 

 physis ligamentous. Hallux large and opposable. Terminal phalanges later- 

 ally compressed and pointed, without clefts. Ampliiproviverra. 



(Miocene, Santa Cruz formation, Patagonia, A. niazaniana, A. minuta.) 

 (b) Alisphenoid bulla absent. 



I. Dental formula A ? , \, %, A. Protocone well developed on Ml, and M^, absent on 

 Mi. MA with vestigial protocone and metacone. Posterior premolar not greatly 

 enlarged, in the inferior series not exceeding the median premolar in size. 

 Talonid of M T small and basin-shaped, with a single high cusp on its posterior 

 rim. Palate imperforate. Mandibular symphysis fused. Hallux reduced, not 

 supporting phalanges. Terminal phalanges laterally compressed, sharply 

 pointed, and slightly cleft at tips. Prothylacynus. 



(Miocene, Santa Cruz formation, Patagonia, P. patagonicus.') 

 B. Skull brachycephalic. 



(a) Alisphenoid not dilated to form a bulla. 



I. Dental formula f , \, |, A. Protocone on upper molars reduced. MA bicuspidate 

 with paracone and antero-external style. Posterior premolars greatly enlarged. 

 Talonid of Mj with single conical cusp. Palate imperforate. Mandibular sym- 

 physis fused. Hallux unknown. Terminal phalanges round, blunt, and broadly 

 fissured at the tips. Borhyeena. 



(Miocene, Santa Cruz formation, Patagonia, B. tuber ata, B. excavata.) 



The determination of the marsupial affinities of the Santa Cruz dipro- 

 todonts rests almost entirely on their close resemblance to Ccenolestes. 

 The discussion of the classification adopted is more conveniently post- 

 poned to a later chapter, but it may be remarked in passing that all are 

 referred to one family, the Caenolestidae, so named from its best known 

 and only surviving representative, Ccenolestes. 



